Climate Watch

By Rick Thoman Alaska Climate Specialist Alaska Center for Climate Assessment and Policy International Arctic Research Center/University of Alaska Fairbanks

You may have learned in school that at or above the Arctic Circle (about 66.5° North latitude) on winter solstice the sun does not rise and on summer solstice there’s 24 hours of sunshine. Now that may pass for “close enough” in the Lower 48, but many western Alaskans have firsthand experience to know that is not exactly true.

Kotzebue, which is 20 miles north of the Arctic Circle, has over one and half hours of sunshine on winter solstice. And

Shishmaref, seven miles south of the Arctic Circle, has four weeks of 24 hour per day sunshine in June and early July.

It turns out that the latitude for no sunrise on winter solstice and 24 hours of sun on summer solstice are displaced by about 60 miles from the Arctic Circle (north in winter, south in summer) due to the refraction of the sun’s light by Earth’s atmosphere. There is no place on planet Earth where there is one day with no sunrise and one day with 24 hours of sun.

From the weather and climate perspective, the amount of possible sunshine is much less important than the amount of heating by solar energy at a particular day, and this varies much less than the amount of daylight. In fact, all across western Alaska the amount of solar heating on winter solstice, and for several weeks before and after, is very close to none at all. When we take into account the snow cover that is present on winter solstice but not at summer solstice, Nome on December 21 receives about 0.1 percent of the total solar energy received on June 21. To put that difference into perspective, if summer solstice solar heating is a $100 bill, what we get on winter solstice is one thin dime. And on that note, I’d like to wish happy and safe holidays to all the Nome Nugget readers. Climate Watch will be back in the New Year to take on whatever weather and climate comes our way.